release 4.2.x for freeze_utxo and aiorpcx updates

[chappjc]

Since you are keeping fairly well in sync with upstream Electrum, it would be helpful if a 4.2.x release could be made. For me this would help with aiorpcx incompatibilities (0.22 supported upstream, but not at 4.0.9) as well as providing the freeze_utxo RPC that is absent in 4.0.9.

Apologies for making a request in a Github issue, but it does appear the aiorpcx issue is resolved upstream so that could be resolved for end users with a new release.

Thanks for maintaining this project @pooler!

[pooler]

Version 4.2.2.1 is now available for download.